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Full text of "Text Book Of Mechanical Engineering"

Appendix VI.

Then, from the figure

1107

or

y

Fraction for acceleration scale =  JveL scale {f^-

distance scale fraction

P. 302. Flexible Couplings.  It often happens that
shafts, though made truly in line when first erected, may take
small relative movements through lack of rigidity in the supports,
thus causing a tendency to breakage if firmly coupled. Deviations
that are small and unimportant at low speeds may become very
troublesome at high ones, partly because the rate of change of
deviation is greatly increased, and partly, also, because the
amount of deviation may itself be multiplied by centrifugal force.
As examples we have the very potent one of the breakage of
propeller shafts of ships, no doubt largely on account of the
flexibility of the hull ; and the necessity of universal couplings in
motor-cars, to prevent breakage due to bending of the frame, as
well as to compensate for slight inaccuracies of workmanship that
would otherwise cause hot bearings. When engines and dynamos
are coupled direct, there is the same danger, for a very small
inaccuracy that would not be apparent on a more slow-running
shaft would soon cause heating or knocking on account of the
high speed.

Of the flexible couplings illustrated in Fig. 973 the first two
are intended for marine shafts, and the third for dynamo work.
Brotherhood's coupling consists of a large hollow casting D, to
which is bolted a thin corrugated steel disc E; and while the
casting is bolted to the shaft A, the disc is bolted to the shaft B.
The shafts butt together on a spherical surface c, and any relative
bending of the two is met by a buckling of the disc E to of
course a very slight extent. The faults of this coupling are its
large size and the fact that it cannot well support an axial tension.
In Alley's coupling the shafts F and G are supplied with solid